Heredity and Variation Notes
* The branch of biology which studies the transfer of characteristics of organisms from one generation to the next ,and genes in particular , is called 'genetics'.
* Organisms produced by asexual reproduction show minor variations .
* Offspring produced through sexual reproduction show comparatively greater variation .
What is heredity ?
Ans- Transfer of characteristics from parents to offspring is called heredity .
* Information necessary for protein synthesis in the cell is stored in DNA.
* The segment of DNA which contains all the information for synthesis of a particular protein is called 'gene' for that protein .
Chromosomes
* The structure in the nucleus of cells that carries the heredity characteristics is Called the chromosomes.
* Chromosomes are made up of nucleic acids and proteins .
* Genes which contain the information about hereditary characteristics in coded form are located on chromosomes ,
* Each chromosomes is made up of DNA
* There is a constricted region on each chromosome , This divides the chromosome into two parts Each part is called an Arm
*The centromere has a specific position in each chromosomes
* Types of chromosomes
* A chromosomes may have either equal arms or unequal arms , this depend upon the position of centromere , the chromosomes is of four types :
1, Metacentric Chromosomes : The chromosomes in which the centromere is near the middle and the two arms are almost equal in length , is called metacentric Chromosomes .
2. Sub-metacentric chromosomes : The chromosome in which the centromere is slightly away from the middle point and consequently its one arm is slightly short and the other arm is slightly long , is called sub-metacentric chromosomes .
3. Acrocentric Chromosome : The chromosome in which the centromere is near the end and consequently its one arm is very short and other is very long ., is called acrocentric chromosomes
4. Telocentric chromosomes : The chromosomes in which the centromere is at the tip of chromosome and the arms are on one side only , is called telocentric chromosomes .
